Turbochargers are provided on an engine to deliver air to the engine intake at a greater density than would be possible in a normal aspirated configuration. This allows more fuel to be combusted, thus boosting the engine's horsepower without significantly increasing engine weight.
Generally, turbochargers use the exhaust flow from the engine exhaust manifold, which exhaust flow enters the turbine housing at a turbine inlet, to thereby drive a turbine wheel, which is located in the turbine housing. The turbine wheel provides rotational power to drive the compressor wheel and thereby drive the compressor of the turbocharger. This compressed air is then provided to the engine intake as referenced above.
Referring in more detail to a representative turbocharger 10 shown in the cross-sectional view of FIG. 1, the turbocharger 10 includes a turbine housing or casing 12 having a volute 14 extending circumferentially therein, a compressor housing 16 and a compressor volute 17, and a turbine wheel 18 and a compressor wheel 19 that are rotatably connected together by a shaft 21. The shaft 21 is supported by a bearing system 22 which is supported within a central bearing housing 23 disposed between the turbine housing 12 and the compressor housing 16. The bearing housing 23 defines a bearing chamber 24 which extends axially between the compressor housing 16 and turbine housing 12 to allow the shaft 21 to extend axially therebetwen so that rotation of the turbine wheel 18 drives rotation of the compressor wheel 19 during operation of the turbocharger 10.
The bearing system 22 typically includes a journal bearing 25 positioned within the bearing chamber 24 to provide radial support to the rotating shaft 21.
FIGS. 2 and 3 illustrate one example of a known bearing configuration, which is currently in commercial use. In this configuration, a semi-floating ring bearing 30 is provided which mounts within the bearing chamber 24 so that it is located radially between a radially inward-facing chamber surface 31 of the bearing housing 23 and a radially outward-facing shaft surface 32 of the shaft 21. The bearing 30 includes stop formations 33 on at least one of the bearing ends, wherein a locking pin engages between the bearing housing 23 and formations 33 to prevent rotation of the bearing 30 relative to the bearing housing 23 during shaft rotation. However, this semi-floating ring bearing 30 is able to float or move radially to a small extend during shaft rotation.
To dampen radial movements caused by shaft rotation, a fluid such as oil is supplied to the bearing chamber 24 which is able to flow through the ring bearing 30 to the inside thereof. The bearing 30 includes a cylindrical bearing wall 34 which defines inner and outer cavities 35 and 36 wherein the wall 34 includes ports 37 through which oil may flow between the cavities 35 and 36. The opposite ends of the bearing 30 include squeeze film dampers 39 defined by outer bearing surfaces 40 that respectively form an outer fluid film 41 of oil. Additionally, the bearing ends include journal bearings 42 defined by inner bearing surfaces 43 that respectively define an inner fluid film 44 of oil. The outer and inner films 41 and 44 form between the outer and inner bearing surfaces 40 and 43 and the opposing shaft surface 32 and chamber surface 31.
This semi-floating ring bearing 30 is known and in commercial use although such bearing 30 also exhibits some characteristics which may be undesirable. For example, semi-floating ring bearings are prone to exhibit one or more subsynchronous motions having a large amplitude which may arise during shaft rotation over an extended range of operating speeds. Further, the inner bearing films may have large cross-coupled stiffness coefficients which can be a typical driver of instability in a rotor-bearing system. Still further, the damping coefficients of the squeeze film dampers are non-linear with the rotor's dynamic response amplitude, are sensitive to oil supply pressure and temperature and are difficult to predict.
In other types of bearings, tilting pad bearings are commonly used in high performance turbomachinery because they have proven stability characteristics. For example, tilting pad bearings do not generate cross-coupled stiffnesses.
In another example, tilting pad bearings provide the same rotordynamic advantages as the tilting pad bearings. Typically, tilting pad bearings are machined as one piece and eliminate pivot wear, contacts stresses, and pad flutter, and minimize the stack-up of manufacturing tolerances. Pads machined integrally with the bearing offer a compact bearing unit which is easy to install.
Despite the foregoing, disadvantages can still exist with known bearing configurations.
The invention relates to an improved bearing for a turbocharger wherein the inventive bearing preferably is a semi-floating ring bearing, which has compliant structural dampers installed between the outer bearing surface and the inner surface of the bearing chamber so as to eliminate squeeze film dampers. These compliant structural dampers can be formed as metal mesh dampers or bump foil dampers which are effective to dissipate mechanical energy from structural damping and dry-friction.
In one embodiment, metal mesh dampers provide distinctive advantages over squeeze film dampers. For example, such metal mesh dampers are not dependent upon lubricant supply like squeeze film dampers such that there is no requirement for oil and no stiffness and damping variations due to the operational characteristics of the supplied oil. The metal mesh dampers also provide stiffness as well as damping, and can handle extreme temperature differences since there is no variation in stiffness and damping due to temperature changes. Still further, the stiffness and damping coefficients can be selectively varied and controlled by changing the metal mesh material, geometry and mesh density depending upon the operating conditions encountered in the bearing chamber during shaft rotation. The metal mesh dampers also provide maximum damping at lower frequency ranges, wherein rotordynamic instability frequencies are significantly lower than the rotor synchronous frequency or shaft rotational frequency.
In another embodiment, the compliant structural damper may be a bump foil damper which also provides structural stiffness and frictional damping. This thereby lowers transmitted forces and increases bearing/machinery life.
As described further herein, the inventive bearing provides advantages over known bearing configurations.
Other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.
Certain terminology will be used in the following description for convenience and reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the arrangement and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.